Two notorious north Dublin brothers nicknamed 'The Taliban' have returned to Dublin after spending years on the run in Europe and Northern Ireland.
The pair have been spotted in the Edenmore and Coolock areas of the capital in recent weeks.
It is understood they have been collecting money in relation to a massive heroin and cocaine dealing network.
The brothers, aged 32 and 30, are wanted for questioning in relation to a spate of killings including two double murders.
Gardai have spent years working with the PSNI monitoring the pair's activities, but so far they have managed to avoid serious convictions.
"It is a worrying development that these two evil individuals feel confident enough to be operating in Dublin again as they are wanted for questioning in relation to a litany of murders," a source said.
"When they first came back they would only spend an hour or two in Dublin before fleeing across the border, but now they're even staying overnight which shows that they're beginning to feel more and more comfortable."
The brothers are the chief suspects for the savage slayings of Ballybough men Joseph Redmond (25) and Anthony Burnett (31), who were shot and their bodies burned in a car in a forest near Dundalk, Co Louth, in March 2012. An adjourned inquest heard both men died from gunshot wounds to the head and that their bodies were found "completely charred".
The other double murder in which the brothers are chief suspects is that of cousins Glen Murphy (19), of O'Devaney Gardens, and Mark Noonan (23), from Drumalee, both in the north inner city, who were shot dead outside a service station at Tesco Express at the Clearwater Shopping Centre in Finglas in November 2010.
Gardai are satisfied that the cousins were victims of mistaken identity, targeted as part of a Coolock drugs feud in which they had no involvement.
Neither of the victims had any connection with gangland crime, but were shot dead when a "non-sophisticated" tracking device was mistakenly put on a Toyota Avensis car that was owned by Mark Noonan instead of a car belonging to a major criminal.
After their murders, gardai found the device hidden in the rear of the Avensis.
They believe it was planted there on behalf of the major northside criminal who had ordered the hit.
The brothers are also the chief suspects for the murder of small-time criminal James Perdue (22), who was shot dead in Donaghmede in June 2006.
They are further believed to have had some involvement in the slayings of innocent men Warren O' Connor (24), who was stabbed to death in January 2010, and Keith Fitzsimons, who was gunned down in 2006.
'The Taliban' grew up in the Coolock area and were heavily involved in organised burglaries and armed robberies when they were teenagers.
The feared siblings then progressed to contract killings and became the main hitmen for the 'Mr Big' drugs gang.